A data transfer amount of a wireless network has been rapidly increased in recent years. It is because various devices, e.g., a smart phone, a tablet personal computer (PC), or the like, that require machine-to-machine (M2M) communication and a high data transfer amount have been introduced and propagated. To satisfy the required high data transfer amount, a carrier aggregation technique, a recognition radio technique, or the like for effectively using more frequency bands, and a multiple antenna technique, a multiple base station cooperation technique, or the like for increasing data capacity within a limited frequency have recently drawn attention.
In addition, the wireless network has been evolved in a direction of increasing density of a node capable of accessing to an area around a user. Herein, the node implies an antenna (or antenna group), in a distributed antenna system (DAS), separated from other antenna by a certain distance or farther. However, the node is not limited to this definition, and thus can also be used in a broader sense. That is, the node may be a pico-cell eNB (PeNB), a home eNB (HeNB), a remote radio head (RRH), a remote radio unit (RRU), a relay, etc. A wireless communication system having such a node with higher density can provide higher system performance by cooperation between nodes. That is, better system performance can be achieved when one base station controller manages transmission and reception of respective nodes and thus the nodes operate as if they are antennas or an antenna group for one cell, in comparison with a case where the respective nodes operate as an independent base station (BS), advanced BS (ABS), node-b (NB), eNode-B (eNB), access point (AP), etc., and thus do not cooperate with each other. Hereinafter, a wireless communication system including multiple nodes is referred to as a multi-node system.
A node is applicable even if it is defined as an antenna group, irrespective of distance, as well as an antenna group spaced a distance apart from another antenna group. For example, a base station including cross-polarized antennas can be regarded as including a node consisting of an H-pol antenna and a node consisting of a V-pol antenna.
Coordinated multipoint transmission and reception (CoMP) is applicable to a multi-node system. Inter-cell interference can be reduced by applying CoMP to a multi-cell multi-node system, and intra-cell inter-point interference can be reduced by applying CoMP to a single-cell multi-node system.
There are two types of CoMP schemes: a JP (joint processing) scheme and a CS (coordinated scheduling/beamforming) scheme. In the JP scheme, multiple nodes share and transmit data of UE. In the CS scheme, a single node transmits data of a UE cooperates with other nodes by scheduling or by forming transmission beams to reduce interference.
In the multi-node system, a method for a UE to efficiently measure channel information is required.
In the multi-node system, a base station may request the UE to provide channel information feedback to the nodes in the vicinity of the UE. The channel information required by the base station may vary according to purpose/usage.
In the multi-node system, what channel information feedback the UE will provide after measuring a reference signal may be an issue.